Cellulose is a polymer of glucose linked by beta-1,4-gucosidic bonds. Cellulose chains form numerous intra- and intermolecular hydrogen bonds, which result in the formation of insoluble cellulose micro-fibrils. Microbial hydrolysis of cellulose to glucose involves the following three major classes of cellulases: (i) endo-glucanases (EC 3.2.1.4) which cleave beta-1,4-glucosidic links randomly throughout cellulose, molecules also called endo-beta-1,4-glucanases; (ii) cellobiohydrolases (EC 3.2.1.91) which digest cellulose from the non-reducing end, releasing cellobiose; and (iii) beta-glucosidases (EC 3.2.1.21) which hydrolyse cellobiose and low molecular-weight cellodextrins to release glucose.
Beta-1,4-glucosidic bonds are also present in other naturally occurring polymers, e.g. in the beta-glucans from plants such as barley and oats. In some cases, endo-glucanases also provide hydrolysis of such non-cellulose polymers.
Cellulases are produced by many micro-organisms and are often present in multiple forms. Recognition of the economic significance of the enzymatic degradation of cellulose has promoted an extensive search for microbial cellulases, which can be used industrially. As a result, the enzymatic properties and the primary structures of a large number of cellulases have been investigated. On the basis of the results of a hydrophobic cluster analysis of the amino acid sequence of the catalytic domain, these cellulases have been placed into different families of glycosyl hydrolases; fungal and bacterial glycosyl hydrolases have been grouped into 35 families (Henrissat, B.: A classification of glycosyl hydrolases based on amino acid sequence similarities. Biochem. J. 280 (1991), 309-316. Henrissat, B., and Bairoch, A.: New families in the classification of glycosyl hydrolases based on amino acid sequence similarities. Biochem. J. 293 (1993), 781-788). Most cellulases consist of a cellulose-binding domain (CBD) and a catalytic domain (CAD) separated by a linker which may be rich in proline and hydroxy amino acid residues. Another classification of cellulases has been established on the basis of the similarity of their CBDs (Gilkes et al. (1991)) giving five families of glycosyl hydrolases (I-V).
Cellulases are synthesized by a large number of microorganisms which include fungi, actinomycetes, myxobacteria and true bacteria but also by plants. Especially endo-beta-1,4-glucanases of a wide variety of specificities have been identified. Many bacterial endo-glucanases have been described (Gilbert, H. J. and Hazlewood, G. P. (1993) J. Gen. Microbiol 139:187-194. Henrissat, B., and Bairoch, A.: New families in the classification of glycosyl hydrolases based on amino acid sequence similarities. Biochem. J. 293 (1993), 781-788).
An Important industrial use of cellulolytic enzymes is for treatment of paper pulp, e.g. for improving the drainage or for de-inking of recycled paper. Another important industrial use of cellulolytic enzymes is for treatment of cellulosic textile or fabrics, e.g. as ingredients in detergent compositions or fabric softener compositions, for bio-polishing of new fabric (garment finishing), and for obtaining a “stone-washed” look of cellulose-containing fabric especially denim, and several methods for such treatment have been suggested, e.g. in GB-A-1 368 599, EP-A-0 307 564 and EP-A-0 435 876, WO 91/17243, WO 91/10732, WO 91/17244, WO 95/24471 and WO 95/26398. JP patent application No. 13049/1999 discloses a heat resistant alkaline cellulase derived from Bacillus sp. KSM-S237 (deposited as FERM-P-16067) suitable for detergents.
There is an ever existing need for providing novel cellulase enzymes or enzyme preparations which may be used for applications where cellulase, preferably an endo-beta-1,4-glucanase, activity (EC 3.2.1.4) is desirable.
The object of the present invention is to provide novel enzymes and enzyme compositions having substantial beta-1,4-glucanase activity under slightly acid to alkaline conditions and improved performance in paper pulp processing, textile treatment, laundry processes, extraction processes or in animal feed; preferably such novel well-performing endo-glucanases are producible or produced by using recombinant techniques in high yields.